The present invention relates to a wheel balance measuring apparatus which measures the dynamic balance of the tested wheel, and more particularly to a wheel balance measuring apparatus which has a load detector on the bearing thereof for detecting displacement load imparted on the bearing due to weight unbalance during the rotation of the tested wheel.
In more detail, the wheel balance measuring apparatus to which the present invention is applied is equipped with a pair of upper and lower rims to hold the tested wheel therebetween. The lower rim is mounted on a rim support shaft supported by a bearing, to which a detector for detecting displacement load is connected, rotatably about a vertical axis, and the upper rim is spaced upward from this lower rim so as to confront with each other. The upper rim is shiftable along an up-and-down direction so as to change the clearance between the upper and lower rims, and is rotatably supported about the vertical axis. The tested wheel is firmly sandwiched between these upper and lower rims and rotated about the vertical axis. As the tested wheel has weight unbalance, displacement load is imparted on the bearing and the load detector detects this displacement load. Thus, the dynamic balance of the tested wheel is obtained on the basis of thus obtained detection result.
A conventionally known wheel balance measuring apparatus, which measures the dynamic balance of the tested wheel, is equipped with a pair of upper and lower rims to hold the tested wheel therebetween. The lower rim is mounted on a rim support shaft rotatably supported about a vertical axis by the bearing, and the upper rim is spaced upward from this lower rim so as to confront with each other. The upper rim is shiftable along an up-and-down direction so as to change the clearance between the upper and lower rims, and is rotatably supported about the vertical axis. The tested wheel is firmly sandwiched between these upper and lower rims and rotated about the vertical axis. The displacement loads at the upper and lower ends of the bearing are detected by the detectors. Then, the dynamic balance of tile tested wheel is obtained on tile basis of thus obtained detection result.
In such a conventional measuring apparatus, it is necessary to firmly engage the upper rim with the lower rim not to move by the pressure of tile compressed air supplied in the tested wheel during the testing operation. On the contrary, it is also necessary to completely remove the upper rim from the lower rim when the tested wheel is taken out.
For these reasons, a coupling shaft, fixed to the upper rim so as to extend downward from the bottom of this upper rim, is inserted in a coupling hole of the rim support shaft. The upper and lower rims are adjusted to fit to the rim width of the tested wheel, and engaged together to maintain thus adjusted clearance.
The bearing, which supports the rim support shaft, needs to be supported in the following manner. The rigidity of the bearing is low in tile displacement load detecting direction of the detector so that the detector can detect the displacement load effectively, while the rigidity of the bearing is high in other directions. Namely, the bearing is resiliently supported to cause vibration in the displacement load detecting direction of the detector, but is rigidly supported not to cause vibration in other directions.
It is desirable for such a conventional wheel balance measuring apparatus to be applicable to a plurality sizes of tested wheels. It is necessary, in order to realize this, to integrally form a plurality of rims of different diameters so as to adjust tile upper and lower rims to fit to the rim width of any kind of tested wheel. On the other hand, it is not easy to provide a firm fixing structure capable of bearing compressed air in the wheel.
Furthermore, in order to ensure the coupling and detachment, a predetermined tolerance needs to be provided between the coupling shaft and the coupling hole of the rim support shaft. However, when the tested wheel is inflated during the measuring operation, the coupling shaft causes the inclination with respect to the coupling hole. As a result, the upper rim inclines against the lower rim. This induces the measurement error. As the inclination direction cannot be predicted, it was impossible to correct the measurement error caused by this inclination.
Still further, it is actually impossible to support the bearing, which supports the rim support shaft, not to cause any vibration in the directions other than the displacement load detecting direction of the detector. Therefore, vibrations caused in the directions other than the displacement load detecting direction of the detector also cause the measurement error.
Moreover, tile bearing receives impact force in the up-and-down direction when the tested wheel is installed on or removed from the rims. The detector may be damaged or its accuracy may be deteriorated by receiving this impact force.